Ibragim Todashev, a friend of Boston Marathon bombing suspect Tamerlan Tsarnaev, is fatally shot by an FBI agent as he is being questioned about a triple slaying.

WASHINGTON — A friend of purported Boston Marathon bomber Tamerlan Tsarnaev was shot and killed early Wednesday by an FBI special agent in Orlando, Fla., after lunging with a knife and injuring the agent during an interview about the April 15 explosion and an unrelated triple homicide, officials said.

Federal law enforcement sources identified the slain man as Ibragim Todashev, 27, a Chechen immigrant and former martial arts fighter like Tsarnaev. Todashev was being questioned in an apartment by the FBI agent, two Massachusetts State Police troopers and other law enforcement officials.

The interview was underway "when a violent confrontation was initiated by the individual," the FBI office in Boston said in a statement. "During the confrontation, the individual was killed and the agent sustained non-life-threatening injuries." The agent's identity was not released.

The shooting is under review, said FBI spokesman Dave Couvertier in Orlando, and an FBI team was dispatched from Washington headquarters to investigate.

Federal officials said Todashev was being asked primarily about an unsolved Sept. 11, 2011, triple slaying in Waltham, Mass. Officials believe he and Tsarnaev may have had a role in the slayings, in which three men were found with their throats cut and marijuana sprinkled over their bodies.

The officials also had questions about his relationship with Tsarnaev. One of the three Waltham victims, Brendan H. Mess, was described as a close friend of Tsarnaev's. They also believed Todashev had visited Tsarnaev in Boston before the bombings.

Tsarnaev was killed in a police shootout four days after the bombings, and his younger brother, Dzhokhar Tsarnaev, was arrested and charged in the blasts that killed three people and injured more than 260 others.

In the last month, FBI and other law enforcement officials have interviewed a wide range of people who were associated with the Tsarnaev brothers, from the Boston area, New Hampshire and Chechnya, and now in Florida.

One federal law enforcement source said authorities had been talking to Todashev and other Chechen immigrants in the Orlando area for several days, and returned to the apartment Wednesday because Todashev was planning to return to Chechnya soon.

Near the scene of the shooting, Khusen Taramov, 22, who described himself as a friend of Todashev's, told the Orlando Sentinel that Todashev knew Tamerlan Tsarnaev because both were mixed martial arts fighters. Taramov said that Todashev had lived in Boston and had been part of bouts there with Tamerlan Tsarnaev, and that Todashev had last talked to Tsarnaev about a month ago by phone.

Since the bombings, Taramov said, the FBI had been questioning Todashev, and had talked to Taramov as well.

Taramov said he spent most of last week with Todashev because his friend was scared and tired after weeks of nearly constantly being followed and occasionally questioned by FBI agents.

"I was with him every minute. I knew what was going on in his head," he said of Todashev's fear of being linked to the bombings. "To me, it's a setup. This is what he was afraid of. They had nothing.... He was innocent."

Todashev was outraged about the bombings, said three of his friends in Kissimmee, Fla., and stunned to realize he knew both Tsarnaev brothers.

Todashev had a previous run-in with authorities. He was arrested May 4 and charged with aggravated battery with great bodily harm in Orange County, Fla., in a dispute over a parking spot at an outlet mall. According to sheriff's deputies, Todashev said he fought with a man "to protect his knee because he had surgery in March."

A sheriff's report said that two men were fighting and that one, later identified as Todashev, left in a vehicle while the other was on the ground, appeared unconscious and was surrounded by "a considerable amount of blood."

Deputies pursued Todashev, pulled him over and ordered him out of his car at gunpoint, according to the report. The victim, who had a split upper lip and "several teeth knocked out of place," did not want to press charges, the report said.